Posterior to lateral interbody fusion approach with associated instrumentation and implants

ABSTRACT

Methods for accessing a disc space of a patient as a part of an interbody fusion, as well as the tools employed therewith. An exemplary method may include inserting a leading end of an tool into the patient&#39;s back at a location on the posterior surface that is laterally offset from a patient&#39;s spinous process and disc. The tool&#39;s initial entry into the patient may be from a posterior approach. As the tool is advanced along its designated path, it begins to deviate from the posterior approach towards a lateral approach. When the leading end reaches the disc, it may access the disc from a lateral or substantially lateral location. The tool may be used to access the disc location, to remove disc material, to deliver a cutting tool for removing the disc material, and other steps associated with the spinal interbody fusion procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 USC § 119(e) of U.S.Patent Application Ser. No. 62/370,928, filed Aug. 4, 2016 and entitled“POSTERIOR TO LATERAL APPROACH”, which includes screen captures from ananimation prepared by the inventor of the presently described methods.The present application claims the benefit under 35 USC § 119(e) of U.S.Patent Application Ser. No. 62/382,007, filed Aug. 31, 2016 and entitled“POSTERIOR TO LATERAL APPROACH. The present application also claims thebenefit under 35 USC § 119(e) of U.S. Patent Application Ser. No.62/270,013, filed Dec. 20, 2015 and entitled “POSTERIOR TO LATERALAPPROACH FOR INTERBODY SPINAL FUSION”, as well as U.S. PatentApplication Ser. No. 62/214,489, filed Sep. 4, 2015 and entitled“EXPANDABLE INTERBODY FUSION DEVICE”. The disclosure of each of theforegoing is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention generally relates to methods for accessing one ormore discs of the vertebrae, e.g., as part of a spinal interbody fusion,as well as devices for use therewith.

2. The Relevant Technology

Over the past several decades, spinal surgery has increasingly become animportant option available to surgeons and patients in treating issuesrelated to the spine. Because the spine generally provides support andmovement for the body, a problem with the spine (e.g., a back disorder)can disrupt even the simplest life activities. In general, thousands ofsurgical interbody fusions of the spine are performed each year in anattempt to decrease pain and to increase function for the patient.Interbody fusion is a common procedure that attempts to create a bonybridge, or union, between two vertebral bodies to eliminate movementbetween the two individual vertebrae. This loss of motion can becurative for those suffering from a variety of back disorders, includingdegenerative conditions or instabilities.

Many different methods are currently in use by surgeons to accomplishinterbody fusion. Generally, an incision is made, and the disc isexposed and the disc material is removed. The end plates of thevertebral bodies may be stripped of any remaining cartilage thusexposing the bony faces of the adjacent vertebrae. The disc space may befilled with a material compatible with fusion. In most cases, the discspace may also be filled with some sort of implant, or spacer, intendedto prevent narrowing, filling, or collapse of the disc space during thefusion process. Generally speaking, the greater the agitation, scraping,or other “damage” to the vertebral endplates, the greater the biologicefforts effected by the body to heal the damage, thus creating thefusion. Current approaches used by spinal surgeons to access the discspace and accomplish an interbody fusion typically include anterior,posterior, posterolateral, or a lateral approach.

Surgical techniques currently available are reliable, but they are notwithout risk and potential complications. Reducing risk without reducingthe effectiveness of the surgery is desirable. In addition, it would beadvantageous if new techniques better limited the amount of surgicaltrauma to the patient, reducing recuperation and healing times. As such,there exists a continuing need for improved techniques for performinginterbody spinal fusion.

BRIEF SUMMARY

In one aspect, the present invention relates to methods for accessing adisc of a patient's vertebrae as part of a spinal interbody fusion.Anterior approaches require mobilization of the vascular structures inthe region and can cause injury to the sympathetic plexus. Posterior andposterolateral approaches can present a risk to nerve roots as well asto the bones of the spine which must be navigated around as thepractitioner accesses the location of the disc to be removed and fused.A lateral approach, while lessening such risk to nerve roots and bonetissues adjacent the location to be accessed, presents increased risk tothe colon and to the lumbar plexus. The present disclosure proposes anew technique that would begin as a posterior approach, but becomes alateral approach as the disc location is actually approached, hereinreferred to as a posterior to lateral approach. Such method may providethe surgeon with a technique that can be performed reliably, with anacceptable safety profile, and predictable outcomes. The procedure isdesigned to be capable of being performed in a minimally invasivemanner. It is anticipated that the procedure would be safe and reliable,with safety and reliability characteristics improved over currenttechniques, so as to be suitable for use by both spine surgeons, as wellas interventional pain management doctors.

In the novel posterior to lateral approach, the disc location isaccessed directly laterally, or nearly directly laterally (e.g., someangular offset from directly lateral may be acceptable) after an initialentry from the posterior surface (i.e., the back) of the patient.According to one embodiment, one such method may include inserting aleading end of a tool (e.g. a cannula) into the patient's back at alocation on the posterior surface that is laterally offset from apatient's midline (e.g., midline and spinous process). The tool maybegin with an initial entry into the patient from a posterior (orperhaps more accurately posterolateral) approach relative to the disc.The tool may continue to be advanced along a path which may begin todeviate from the posterior (or posterolateral) approach towards alateral approach as the tool is advanced toward a lateral aspect of thedisc. When the leading end of the tool actually reaches the disclocation, it may access the disc location from a location that islateral relative to the disc location. The tool may be used to accessthe disc location, to remove disc material, to deliver a cutting toolfor removing the disc material, and other steps associated with thespinal interbody fusion procedure performed from a lateral perspective.

In an embodiment, the leading end of a guide wire may be inserted intothe patient's back at a location on the posterior surface that islaterally offset from the midline. The guide wire may be advanced to thelateral aspect of the disc, or through the lateral aspect of the disc,into the central portion of the disc. The tool may then be inserted overthe guide wire into the patient from the same offset posterior startinglocation. The tool may continue to be advanced along the pathestablished by the guidewire which may begin to deviate from theposterior approach towards a lateral approach as the tool is advancedtoward a lateral aspect of the disc. When the leading end of the toolreaches the lateral aspect of the disc, the tool, or a subsequent toolmay be used to access the disc location, to remove disc material, todeliver a cutting tool for removing the disc material, and/or othersteps associated with the spinal interbody fusion procedure performedfrom a lateral perspective.

A posterior to lateral approach has several distinct advantages becauseit may mitigate some risks associated with other approaches typicallyused in spinal interbody fusion procedures. For example, an anteriorapproach requires retraction of a peritoneal sac and large blood vessels(e.g. left common iliac vein) in order to access the disc. Access to thelumbar disc is difficult using a posterior approach because thepatient's spinal canal, including the contained nerve roots, otherstructures, and bone of the patient (including the facet joints) blockeasy access to the disc. As a result, lamina must be removed and nerveroots retracted before the disc can be accessed. A lateral approachinitially presents a risk to a patient's colon, which must be carefullybypassed to access the disc. The posterior to lateral approach describedherein is designed to avoid damage and risk to these structures. Forexample, the posterior to lateral approach may be performed in a mannerso that the pathway only passes through the patient's skin and muscle(e.g., psoas muscle) to access the disc, making the approach potentiallymuch less invasive, while maintaining the advantages of accessing thedisc space from a lateral perspective.

Because the posterior to lateral approach may be less invasive, onlypassing through muscle tissue, which can easily be parted to one side orthe other, without necessarily cutting or damaging the muscle, thehealing time for a patient undergoing spinal interbody fusion using theposterior to lateral approach may be far less than other availableapproaches. In fact, for many patients such a procedure may be performedon an outpatient basis.

In another embodiment according to the present disclosure, the methodmay 7 include measuring a distance from a point between the patient'sskin and the patient's spinous process to the center of the disc basedon a scan (e.g., preoperative), and securing a device that may rotateover a posterior surface of the patient's back with a trailing end of atool coupled to the device. The device may include an arm which may ormay not rotate having a length that is based on the measured distancefrom a desired starting point located between the spinous process andthe surface of the skin to the disc center (determined from the scan).In an embodiment, the starting point for the measured distance may bethe tip of the spinous process. A leading end of the tool may beinserted into the posterior surface of the patient's back along apredetermined path that begins (during initial entry) as a posteriorapproach to the disc. Once the tool is inserted, the tool may beadvanced along the predetermined path, which deviates from the posteriorapproach towards a lateral approach as the tool is advanced from theposterior surface until it reaches a lateral aspect of the disc. Thetool may be used to access the disc and perform at least a portion ofthe spinal interbody fusion (e.g., deliver a cutting tool for removingthe disc material, actually removing the disc material, delivering animplant into the disc space, etc).

In another aspect, the present disclosure is directed to a cuttingdevice (e.g., for use with a tool as described herein) for clearing adisc space of a patient's vertebrae between vertebral endplates of thevertebrae as part of a spinal interbody fusion. Such a cutting devicemay include a straight or flexible drive shaft, which may be cannulatedto pass over a guide wire. A retractable blade may be provided at thedistal end of the shaft. The retractable blade may be operably coupledto an extension mechanism at a proximal end of the shaft (e.g., so as tobe easily manipulated by the practitioner) that is configured to adjustan angle that the blade extends from the distal end of the shaftrelative to a longitudinal axis of the device. In other words, theextension mechanism may allow the blade to be selectively extended fromthe distal end of the device, at a desired angle thereto, so that uponrotation of the blade, a given radius (or diameter) cut or clearingaction results. The blade may be operably coupled to an actuatingmechanism that allows the practitioner to selectively rotate the blade(e.g., a quick connector or similar connection to a drill or other powersource for rotating the shaft and blade).

The use of a guide wire placed across the disc space in a lateral, orside-to-side orientation, may help to maintain the cutting device in itsdesired location during cutting. In order to more securely control thepath of the cutting device, particularly while the device is actuallycutting, the guide wire may have a feature on the leading end whichallows the leading end of the guide wire to be captured and secured.This feature may be as simple as a small sphere or other protrusion onthe leading end of the guide wire, or a similar feature. In order tosecure the leading end of the guide wire, it first traverses the discspace in a lateral orientation. The wire is advanced such that a portionof the wire, including the leading end with its capture feature mayextend beyond the lateral confines of the disc and the annulus. In thelumbar spine, the tip of the end of the guide wire may of necessity,extend beyond the confines of the disc, and even into the psoas musclefor a distance sufficient to allow the wire to be captured.

The practitioner may then place a capturing tool into the psoas muscleon the same side of the leading end of the guide wire from a posterioror posterolateral approach. The capturing tool may be advanced along astraight path until the leading end of the capturing tool is near thelocation of the leading end of the guide wire. The leading end of theguide wire may then be captured and secured by the capture tool. In oneembodiment, the capture tool may include a loop made from metal or othermaterial that is initially withdrawn into a containment sleeve. The loopmay be extended out of the end of the S containment sleeve (e.g., atube) and the loop then expands into a circular, or other shape. Thisloop then becomes a target through which the end of the guide wire ispassed. Once the end of the guide wire has passed through the loop(e.g., including the capture feature on the end of the guide wire), theloop may be withdrawn back inside the containment sleeve or otherwise atleast partially retracted until the loop has effective captured andsecured the end of the guide wire. The capture tool may remain securedto stabilize the end of the guide wire, and prevent it from migrating,until the cutting process has been completed. Stabilizing the end of theguide wire in this or a similar manner may prevent the wire frommigrating and keep the cutting device from deviating from a path desiredby the practitioner.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto specific embodiments thereof which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a cross-sectional scan through a patient's body, showing thevarious structures near the vertebrae and disc to be fused.

FIG. 2A shows the scan of FIG. 1, illustrating an exemplary posterior tolateral approach to the disc, reducing risks to adjacent structures ascompared to a posterior approach, or a lateral approach.

FIG. 2B is a perspective view of the torso of an exemplary patient,showing the pathway of an exemplary posterior to lateral approach to thedisc.

FIG. 3A schematically shows the initial stages of an exemplary posteriorto lateral approach, e.g., using a rotating arm with a rigid tool havinga fixed curvature attached at a distal end of the rotating arm, andanother end of the rotating arm being secured at a location that isoffset from the patient's spinous process, the distal end of therotating arm being offset relative to the spinous process.

FIG. 3B schematically shows a more advanced stage of the posterior tolateral approach of FIG. 3A, with the leading end of the tool reachingthe lateral aspect of the disc.

FIG. 3C schematically shows an alternative posterior to lateralapproach, similar to that of FIGS. 3A-3B, but in which the end of therotating arm is secured over the patient's spinous process, rather thanbeing offset therefrom, so as to cause the leading end of the cannula toapproach the lateral aspect of the disc somewhat differently than shownin FIG. 3B.

FIG. 4A is a perspective view of a rigid cannula having a fixedcurvature, such as may be used to follow the pathway shown in FIGS.2A-2B, or follow the pathway of the tool shown in FIGS. 3A-3C.

FIG. 4B is a perspective view of a flexible cannula, comprising a cablewhich can be selectively actuated to cause the cannula to assume acurved configuration, with the flexible cannula shown in its straightconfiguration.

FIG. 4C is a perspective view of the flexible cannula of FIG. 4B, butwith the flexible cannula shown in its curved configuration.

FIG. 5 shows a scan similar to that of FIG. 2A illustrating an exemplarypathway that a flexible cannula such as that of FIGS. 4B-4C may beadvanced along.

FIG. 6A shows a perspective view of an exemplary hinged cannulacomprising a mechanical linkage, with the hinge shown in the straightposition.

FIG. 6B is a cross-sectional view through the hinged cannula of FIG. 6A.

FIG. 6C is a perspective view of the hinged cannula of FIG. 6A, with thehinge shown in the angled configuration.

FIG. 6D is a cross-sectional view through the hinged cannula of FIG. 6C.

FIG. 7 shows a scan similar to that of FIG. 5, illustrating an exemplarypathway that a hinged cannula such as that of FIGS. 6A-6D may beadvanced along.

FIG. 8A is a perspective view of an exemplary pre-stressed cannula whichmay be used with an outer sleeve or inner stylet which can be positionedover or within the pre-stressed cannula to hold the pre-stressed cannulain a straight configuration.

FIG. 8B is a perspective view of the pre-stressed cannula of FIG. 8A,shown with the outer sleeve retracted from over the pre-stressed portionof the cannula, so that the pre-stressed portion defaults to its curvedconfiguration.

FIG. 8C is a cross-sectional view through the pre-stressed cannula ofFIG. 8A.

FIG. 9A is a perspective view of an exemplary cutting device in which atleast a portion of the drive shaft is flexible to better allow itsfollowing any of the posterior to lateral approaches described herein.

FIG. 9B is a close up view of the distal end of the cutting device ofFIG. 9A with the blade shown retracted into the distal end of thecutting device.

FIG. 9C is a close up view of the distal end of the cutting device ofFIG. 9A with the blade shown extended laterally from the distal end ofthe cutting device.

FIGS. 10A-10C show a cutting device with one or more blades and acannulation which allows the cutting device to pass over a guide wire,further showing exemplary stop mechanisms to limit the travel of theblade(s) within the disc space.

FIGS. 11A-11C show various views of how a capture device may be used tostabilize the leading end of the guide wire in preparation for thecutting process.

FIGS. 12A-12E show various views of a method and device where a guidingdevice is placed over the patient's back, and the tool is guided throughinsertion and advancement from a posterior or posterolateral approach toa lateral approach.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

The present invention relates to methods used for accessing a disc spaceof a patient as a part of an interbody fusion procedure, as well as thetools used for clearing the disc space of the patient between vertebralendplates of the vertebrae as a part of such an interbody fusion. Such amethod may include inserting a leading end of a tool into the patient'sback at a location on the posterior surface that is laterally offsetfrom a patient's midline (e.g., spinous process). The tool's initialentry into the patient may be from a posterior approach relative to thedisc (although laterally offset as described, so as to perhaps mostaccurately be described as posterolateral), but as the tool is advancedalong its designated path towards the lateral aspect of the disc, orafter it has fully advanced to the lateral aspect of the disc, the pathis deviated from the posterior approach towards a lateral approach tothe disc. When the leading end of the tool actually reaches the disclocation, it may access the disc location from a location that islateral (or substantially lateral) relative to the disc location. Thetool or a subsequently placed tool may be used to access the disclocation, to remove disc material, to deliver a cutting tool forremoving the disc material, and other steps associated with the spinalinterbody fusion procedure.

Another aspect of the present disclosure relates to methods foraccessing the disc space of a patient that may include measuring adistance from a point between the skin and the patient's spinous processto the disc center from a scan (e.g., preoperative scan), and thensecuring a guiding device (which may or may not rotate) over a posteriorsurface of the patient's back to a tool. The guiding device may includean arm having a length that is based on the measured distance from thepoint previously determined (e.g., between the spinous process and thedisc center). In some embodiments, the arm may be rotatable. A leadingend of the tool may be inserted into the posterior surface of thepatient's back. Once the tool is inserted, the tool may be advancedalong the predetermined path, which begins as a posterior (orposterolateral) approach but deviates from the posterior approachtowards a lateral approach as the tool is advanced from the posteriorsurface until it reaches a lateral or substantially lateral aspect ofthe disc. The tool or a subsequent tool may be used to access the discand perform at least a portion of the spinal interbody fusion from alateral perspective (e.g., deliver a cutting tool for removing the discmaterial, actually removing the disc material, delivering an implantinto the disc space, etc.).

In some embodiments, a guiding device may be placed on the back of thepatient which performs a similar function to a rotating arm. In thisembodiment the guiding device may include a curved tunnel, groove, tubeor similar configuration with a radius of curvature substantially equalor at least based on the measurement from the center of the disc to thetip of the spinous process or other desired location there between. Theguiding device is placed on the skin posteriorly so that the includedcurve guides the tool into the skin along an arc as determined by theradius previously measured. The tunnel portion of the guide can beadjusted to compensate for the individual patient. For example, if thepatient is thin and without an additional fatty layer between the skinand the spinous process, the entry point may be directly lateral to thetip of the spinous process, and the radius of curvature will likely bethe distance between the tip of the spinous process and the center ofthe disc. If the patient has a substantial fatty layer then the entrypoint on the skin will be moved posterior from the disc space, and mayalso move medially as the fatty layer increases. This movement away fromthe disc (i.e., posteriorly and medially) requires an adjustment in thestarting angle of the insertion tool such that the tool always followsthe same arc determined by the central point located on the tip of thespinous process, or other desired starting reference point, as well asthe radius determined by the distance to the center of the disc. Theguiding device may be secured in place, such as to the operating table,after placement to reduce the risk of the guiding device changingposition during the remainder of the procedure.

Another aspect of the present disclosure is directed to a cutting device(e.g., for use with a cannula as described herein) for clearing a discspace of a patient's vertebrae between vertebral endplates of thevertebrae as part of a spinal interbody fusion. Such a cutting devicemay include a straight or flexible drive shaft, and a retractable bladeor blades at the distal end of the shaft. In some embodiments, the shaftmay be cannulated. The one or more retractable blades may be operablycoupled to an extension mechanism at a proximal end of the shaft (e.g.,so as to be easily manipulated by the practitioner) that is configuredto adjust an angle that the blade(s) extend from the distal end of theshaft relative to a longitudinal axis of the device. In other words, theextension mechanism may allow the blade to be selectively extended fromthe distal end of the device, at a desired angle thereto, so that uponrotation of the blade(s), a given radius (or diameter) cut or clearingaction results. The blade may be operably coupled to an actuatingmechanism that allows the practitioner to selectively rotate the blade(e.g., a quick connector or similar connection to a drill or other powersource for rotating the shaft and/or blade(s)).

II. Exemplary Methods and Devices

FIG. 1 shows a cross-sectional scan through a torso portion of anexemplary patient's body 100, showing the various structures near thevertebrae 102 and disc 104 to be fused. Some of the illustratedstructures include the muscles 106, 108, and 110 surrounding thevertebrae 102. Specifically, the muscles may include the erector spinae106, the quadratus lumborum 108, and the psoas major 110 muscles. Thescan also shows the colon 112. Although described principally inreference to the right side of the scan, it will be appreciated that ananalogous posterior to lateral approach may be possible from the leftside, with often symmetrical muscle and other structures present.

FIG. 2A illustrates an exemplary posterior to lateral approach to thedisc 104, overlaid on the scan of FIG. 1. As shown, the entry site 114may be on a posterior surface of the patient's back at location that islaterally offset from a patient's spinous process 116. The path 118 tothe disc 104 may begin as a posterior approach (perhaps most accurately,“posterolateral approach”) relative to the disc 104, but as the path 118advances, it may deviate from such approach towards a lateral approach.Therefore, when the path 118 reaches the disc 104, it may reach alateral aspect of the disc 104.

While FIG. 2A shows the path 118 passing through the quadratus lumborum108 and psoas major 110 muscles, while avoiding the colon 112, it willbe appreciated that the posterior to lateral approach is not limited topassage through those specific muscles. Depending on the structure ofthe patient's back muscles and the type of tool used to access the disc104, the path 118 may be through any of the three major back musclessurrounding the vertebrae 102. Those of skill in the art will alsoappreciate that a muscle's fibers, as living tissue, may be parted fromone another, rather than cut, to allow relatively easy passage throughthe muscles. By avoiding cutting the muscles, the patient may recoversignificantly more quickly from the interbody fusion procedure. Forexample, it may be possible to perform such a procedure on an outpatientbasis, with much faster recovery of a the patient to normal activities.

The entry site 114 and path 118 are shown in a perspective view of thetorso of an exemplary patient in FIG. 2B. As shown, the entry site 114may be a location on the posterior surface of a patient's back that islaterally offset from a patient's spinous process 116. The path 118 tothe disc 104 may initially be a posterior approach relative to the disc104, but as the path 118 advances, it may deviate from a posteriorapproach towards a lateral approach. This allows the approach to avoidhaving to tunnel through or around the sensitive and delicate structuresassociated with the spinal canal, spinal cord, other nerves, and bone ofthe patient typically encountered in a posterior approach or traditionalposterolateral approach. In addition, this approach reduces the dangersto the colon inherent in a strict lateral approach. Injuries to thelumbar plexus can be limited by eliminating the need for additionalretraction as is used in lateral approaches. The posterior to lateralapproach which takes a non-linear route to the disc 104 advantageouslytraverses mostly, if not substantially entirely through muscle tissue.Such a route greatly minimizes risk to the sensitive organs and otherstructures of the patient, while also greatly minimizing damage to thepatient that must be healed during recovery.

FIGS. 3A-3B illustrate an exemplary posterior to lateral approach usingan arm 120 which may rotate and a tool 122 that may be rigid with afixed curvature. The trailing end of the tool 122 b may be attached at adistal end of the arm 120 a, and the proximal end of the arm 120 b maybe secured to a guiding device 124 (which itself may rotate) at alocation that may be laterally offset from the patient's spinous process116. The location of the patient's spinous process may simply beobserved by the practitioner on the patient's back, or determined basedon a preoperative scan, or the like. As shown in FIGS. 3A-3B, thedistance from the spinous process 116 to the center of disc 104 may bemeasured or otherwise determined from a preoperative scan (e.g., MRI orthe like). That distance 126 may be used to determine the curvature ofthe tool 122 used in the procedure. The radius 128 of the arc made bythe tool 122 may be substantially equal to the distance from the spinousprocess to the center of the disc 126. Deviations in the radius ofcurvature of the arc may be necessary, depending on the anatomicaldifferences of individual patients.

However, rather than securing proximal end 120 b of the arm 120 andguiding device 124 on the spinous process 116, in this embodiment, theproximal end 120 b of the arm 120 and guiding device 124 may be offsetfrom the spinous process 116 at a distance 130 substantially equal to orotherwise based on the radius 132 of the disc 104. The radius 132 ofdisc 104 may be determined from a preoperative scan. FIG. 3A shows howthe leading end of the tool 122 a may be set up at the entry site 114 onthe surface of the patient's skin (i.e., the lateral aspect of thepatient's back). FIG. 3B shows how the tool 122 may carefully beadvanced through the skin to the lateral aspect of the disc 104 (e.g.,passing through one or more of muscles 106, 108, 110 as seen in FIG.2A). By offsetting the arm 120 at a location lateral to the midline orspinous process 116, when the leading end of the tool 122 a reaches thedisc 104, the leading end of the tool 122 a may be in a truly lateralorientation relative to the lateral aspect of the disc 104. In otherwords, the leading end of the tool 122 a is on the right (or left) sideof the disc, reaching the most lateral aspect of the disc 104, in a truelateral orientation.

When using such an approach, care should be taken to ensure thatsufficient space is always provided between the patient's colon 112 andthe tool 122. An approach that may result in a substantially lateralapproach to the disc 104, while providing even greater spacing relativeto the colon may be preferred under certain circumstances. An example ofsuch an approach is shown in FIG. 3C, where the proximal end 120 b ofarm 120 is not offset from midline 116. In addition, it will be apparentthat by tightening the radius 128 of curvature associated with path 118,the risk to the colon 112 can be further minimized. Furthermore, theactual introduction and advancement of such a tool 122 may be performedwhile the practitioner observes the process on a real-time scan of thepatient's anatomy, to decrease risk of injury to the colon. Whendeciding whether or not to laterally offset the proximal end of the arm120 b and guiding device 124, the amount of such offset, and theparticular radius 128 to be employed, the surgeon may consult thepreoperative scan to minimize any risk to the colon 112.

FIG. 3C schematically shows an alternative posterior to lateralapproach, similar to that of FIGS. 3A-31B. Similar to the method shownin FIGS. 3A-3B, in FIG. 3C the distance 126 from the spinous process 116to the center of disc 104 (or distance between any other selected pointbetween the skin and the disc 104) may be measured from a preoperativescan. That distance 126 may be used to determine the curvature andlength of the tool 122 used in the procedure. The radius 128 of the arcmade by the tool 122 may be equal to or at least based the measureddistance (e.g., distance from the tip of spinous process 116 to thecenter of the disc 104). However, unlike FIGS. 3A-3B, FIG. 3C shows amethod in which the proximal end 120 b of the rotating arm 120 androtational device 124 may be secured over the patient's spinous process116, rather than being offset therefrom. When the proximal end 120 b ofthe arm 120 and guiding device 124 are secured over the spinous process116, rather than being laterally offset therefrom, the tool 122 may notreach the most lateral aspect of the disc 104, although as shown, theapproach still terminates in a substantially lateral approach. It willalso be apparent that the arc length of tool 122 in FIG. 3C may beshorter than that of 3B.

Devices to be placed through the tool 122, such as a cannula, andsubsequently a cutting device, may advantageously be provided with acurvature similar to the curvature of the tool 122. Any implant insertedinto the cleared disc space may also be advanced as needed along thecurved geometry of tool 122. By not laterally offsetting the proximalend 120 b of the arm 120 and guiding device 124, the risk to thepatient's colon 112 may be further reduced. The practitioner may makeadjustments as necessary to ensure that the entry to the disc space isas close to a true lateral approach as possible to minimize risk tosurrounding structures. It may be desirable to pass a guidewire acrossthe disc space before or after insertion of the tool. The guide wire canbe placed through the insertion device, if cannulated, or through acannula placed over the insertion tool. It would be advantageous if theguide wire is passed across the disc space in a lateral directioncentered in the antero-posterior position where the guide wire travelsfully across the disc space to provide a pathway for the subsequentcutting device or other tools.

If the patient's back is covered by a layer of fat thick enough torender the radius 128 of the arc made by the tool 122 too long so as toput the patient's colon 112 at risk as the tool 122 advances through thepatient's back, then a small incision may be made posteriorly throughthe layer of fat to the depth of the spinous process 116 so that the tipof the spinous process, or other point located between the spinousprocess and the skin can still be used as a measuring point for thecenter of the rotational arc and to reduce the radius of the arc. Suchmay effectively recess the proximal end 120 b of the arm 120 and/orguiding device 124 somewhat below the outer skin surface of the patient,so as to account for the relatively thick layer of fatty tissue over thespinous process 116. Such may reduce the radius 128 as compared tomeasuring from the surface of the skin, better avoiding the colon 112.

When comparing FIGS. 3A-3B with 3C, it will be noted that when theproximal end 120 b of the arm 120 and device 124 are laterally offset(FIG. 3B), the tool 122 may be rotated several more degrees (and have aslightly longer length) in order to reach the lateral aspect of the disc104. The arc length of the tool 122 used in the method shown in FIGS.3A-3B may be at least equal to the value of πr/2, with r being theradius 128 of the arc made by the tool 122. In other words, the arclength may be equal or approximately equal to that defined by 90° ofrotation along radius 128. It will also be noted that although theproximal end 120 b of the rotating arm 120 and rotational device 124 arenot offset in the method shown in FIG. 3C, the entry site 114 of thetool 122 remains laterally offset from the spinous process 116 (althoughthe degree of lateral offset may be less). Although FIGS. 3A-3C showmeasurements, the measurements are merely exemplary of how apractitioner may perform the posterior to lateral approach using arotating arm and a tool 122. Of course, actual measurements may differ,although the shown measurements may be relatively typical.

By way of further example, the disc diameter may be from about 1 inch toabout 3 inches, or from about 1.5 inches to about 2.5 inches (e.g.,about 2 inches). The distance from the center of the disc to be fusedand the tip of the spinous process (as measured on a normalperpendicular plane as shown in FIG. 2B) may be from about 1.5 inches toabout 5 inches, from about 2 inches to about 4 inches, or about 3inches.

When employing the methods illustrated in FIGS. 3A-3C, once the tool 122reaches the lateral side of the disc 104 the tool 122 may be securelydocked thereto, and sequential dilators may be passed over the tool 122until an appropriated sized cannula is docked to the lateral side of thedisc 122. In some situations, the practitioner may push the tool 122through the lateral wall of the disc into the central portion of thedisc to secure the tool 122 in its position. As shown, the distalleading end of tool 122 may include spikes or other projections to aidin docking the tool to the lateral aspect of the disc. Furthermore, asdescribed herein, a guide wire may be passed through disc 104, with theguide wire anchored at the opposite lateral end of the disc. Inaddition, the apparatus (e.g., tool 122, device 124, and the like)located outside the skin may be anchored to the table, after it has beenproperly positioned, to prevent movement during the remainder of theprocedure. As shown

FIG. 4A shows a rigid cannula 140 with a fixed curvature, having adistal leading end 142, a proximal end 144, an outer tubular shaft 146,an inner tubular shaft 148, and an attachment feature 150 for securingthe cannula during use. As shown, the rigid cannula 140 may be used tofollow the pathway 118 shown in FIGS. 2A-2B, or follow the pathway ofthe tool 122 shown in FIGS. 3A-3C. The rigid cannula 140 may be madefrom a variety of materials including metals, plastics, or othersuitable biocompatible materials (e.g., titanium, a cobalt chromiumalloy, or the like). The rigid cannula may include a flexible, orrotating section(s), that can be used to facilitate placement of thecannula in situations where the patient has a large fatty layer. Inthese situations, it may prove difficult to pass the cannula due tointerference from the skin on the opposite side of the patient. Theability to bend or rotate the cannulate at some point along the cannulamay help to prevent this issue.

FIGS. 12A-12E illustrate an embodiment similar to that shown in FIGS.3A-4A, but in which the guiding device is fixed, and provides a curvedtunnel, groove or similar pathway through which the tool 140 passes. Forexample, guiding device 124′ may be placed on the back of the patient,and perform a similar function as the above described rotating arm 124.In this embodiment the guiding device 124′ may include a curved tunnel,groove, tube or similar pathway 125 with a radius of curvaturesubstantially equal or at least based on the measurement from the centerof the disc 104 to the tip of the spinous process 116 or other desiredlocation therebetween. The guiding device 124′ is placed on the skinposteriorly so that the included curve guides the tool 140 into the skinalong an arc as determined by the radius previously measured. The tunnelportion 125 of the guide 124′ can be adjusted to compensate for theindividual patient. For example, if the patient is thin and without anadditional fatty layer between the skin and the spinous process, theentry point may be directly lateral to the tip of the spinous process116, and the radius of curvature will likely be the distance between thetip of the spinous process 116 and the center of the disc 104. If thepatient has a substantial fatty layer then the entry point on the skinmay be moved posterior from the disc space, and may also move mediallyas the fatty layer increases. This movement away from the disc 104(i.e., posteriorly and medially) requires an adjustment in the startingangle of the insertion tool 140 such that the tool always follows thesame arc determined by the central point located on the tip of thespinous process 116, or other desired starting reference point, as wellas the radius determined by the distance to the center of the disc 104.The guiding device 124′ may be secured in place, such as to theoperating table, after placement to reduce the risk of the guidingdevice changing position during the remainder of the procedure.

FIGS. 12A-12E show various settings for radius and angle, as may beselected by adjusting where tool 140 enters the tunnel 125 of guidingdevice 124′. For example, FIG. 12A illustrates a configuration that maybe used where the measured distance (e.g., center of disc 104 to tip ofspinous process 116) is 3 inches, with a 4 inch radius, and a selected16° angle in tunnel 125. FIG. 12B illustrates a configuration that maybe used where the measured distance (e.g., center of disc 104 to tip ofspinous process 116) is 3 inches, with a 3.5 inch radius, the cannulatool 140 is centered, and a selected 32° angle in tunnel 125. In thisillustrated configuration, the cannula radius may not be large enough tomaintain the desired path. FIG. 12C illustrates a configuration that maybe used where the measured distance (e.g., center of disc 104 to tip ofspinous process 116) is 3 inches, with a 4 inch radius, the cannula iscentered, and a selected 36° angle in tunnel 125. As compared to FIG.12B, the cannula radius is now large enough to maintain the desiredpath. FIG. 12D illustrates another configuration that may be used wherethe measured distance (e.g., center of disc 104 to tip of spinousprocess 116) is 3 inches, with a 4 inch radius, and a selected 36° anglein tunnel 125. It will be apparent in FIG. 121) that the cannula tool140 has been shifted laterally in tunnel 125 as compared to that of FIG.12C (which otherwise includes similar settings). In this configuration,the cannula radius still clears the colon, but is far away from themedial axis. FIG. 12E shows a close up view of guiding device 124′,illustrating how indicia 127 may be provided thereon for aiding thepractitioner in selecting a desired radius, angle, or other setting.FIGS. 12B-12D show how the presence of a significant fatty layer may bedealt with, as compared to that of FIG. 12A, where no or only a minimalfatty layer may be present.

A flexible cannula 160 is shown in FIGS. 4B-4C, the flexible cannula 160may include a proximal end 162, a handle 164, an outer tubular shaft166, a cable 168, an inner tubular shaft 170 with slots 172, and adistal leading end 174. The cable 168 may be selectively actuated tocause the flexible cannula 160 to assume a curved configuration. FIG. 4Bshows the flexible cannula 160 in its straight configuration, while FIG.4C shows how the cable 168 may be actuated so the flexible cannula 160assumes its curved configuration. The cable 168 may be actuated by themovement of the handle 164 longitudinally relative to the outer tubularshaft 166 toward the proximal end 162 of the flexible cannula 160 (i.e.,pulling handle 164 back, proximally). This movement may cause the cable168 to tension, closing slots 172 in the inner tubular shaft 170 as thecable is tensioned, and the inner tubular shaft 170 may then curve asshown.

FIG. 5 shows how a flexible cannula 160 such as that of FIGS. 4B-4C maybe used to access the disc 104. The entry site 114 of the flexiblecannula 160 may be on the posterior surface of the patient's back at alocation that is laterally offset from a patient's spinous process 116.The flexible cannula 160 may be initially inserted in its straightconfiguration, as shown in FIG. 4B, and the initial approach of theflexible cannula 160 to the disc 104 may be a posterior orposterolateral approach relative to the disc 104. When the flexiblecannula 160 is in the region of the patient's back about the psoas major110 muscle, the cable 168 may be actuated so the flexible cannula 160assumes its curved configuration, as shown in FIG. 4C. In its curvedconfiguration, the approach of the flexible cannula 160 to the disc 104may deviate from the posterior or posterolateral approach towards alateral approach, and the distal leading end 174 of the flexible cannula160 may attach to the lateral aspect of the disc 104 directly, or nearlydirectly, lateral (i.e., lateral or substantially lateral).

In some embodiments, the practitioner may place a flexible straightguide wire from a posterior position through the identified musculature,including the psoas muscle, until the guide wire reaches the lateralaspect of the disc. The guide wire may be passed through the lateralaspect of the disc into the center of the disc to secure the leading endof the guide wire. The flexible cannula 160 may then be passed over theguide wire, through the muscles, towards the lateral aspect of the disc104. The flexible cannula 160 may be advanced until the leading end ofthe cannula approaches the lateral aspect of the disc, or even until theleading end touches or passes into the disc itself. At this point, or atany previous point along the path of insertion along the guidewire, theflexible cannula 160 can be made to assume a curved configuration,either in whole or in part. The flexible cannula may displace thesurrounding muscle tissue during this maneuver until the tip of theflexible cannula assumes its desired relationship to the disc directlylaterally or substantially laterally. The guide wire may or may not beremoved at this point. With the leading end of the cannula directedlaterally, the guidewire can be advanced, directly laterally, orsubstantially laterally, across the disc space, to exit on the farlateral side. Preferentially, the guide wire should be placedequidistant from the front and back of the disc.

As shown in FIGS. 11A-11C, in order to more securely control the path ofthe cutting device, particularly while the device is actually cutting,the guide wire 215 may have a feature on the leading end which allowsthe leading end of the guide wire to be captured and secured. Thisfeature may be as simple as a small sphere or other protrusion 223 onthe leading end of the guide wire 215 or a similar feature. In order tosecure the leading end of the guide wire it traverses the disc space 104in a lateral orientation. The wire 215 is advanced such that a portionof the wire, including the leading end (with its capture feature 223)extends beyond the lateral confines of the disc 104 and the disc annulus104 a. In the lumbar spine, the tip of the end of the guide wire 215 mayof necessity, extend into the psoas muscle for a distance sufficient toallow the wire to be captured.

The practitioner may then place a capturing tool 221 into the psoasmuscle 110 on the same side of the leading end of the guide wire 215from a posterior or posterolateral approach. The capturing tool 221 isadvanced along a straight path until the leading end 225 of thecapturing tool is near the location of the leading end of the guide wire215. The leading end of the guide wire 215 is then captured and securedby the capture tool 221. In one embodiment, the capture tool 221includes a loop 226 made from metal or other material that can bewithdrawn into a containment sleeve 228. The loop 226 is extended out ofthe end of the containment sleeve 228 during capture, and the loop 226expands upon extension into a circular, or other loop shape. This loop226 then becomes a target through which the end of the guide wire 215 ispassed (FIG. 11B). Once the end of the guide wire 215 has passed throughthe loop 226 (e.g., including the capture feature 223 on the end of theguide wire 215), the loop 226 is at least partially withdrawn backinside the containment sleeve 228 until the loop has effective capturedand secured the end of the guide wire 215 (FIG. 11C). The capture tool221 remains secured to stabilize the end of the guide wire 215, andprevent it from migrating, until the cutting process has been completed.Stabilizing the end of the guide wire in this or a similar manner mayprevent the wire from migrating and keep the cutting device fromdeviating from a path desired by the practitioner.

The flexible cannula 160 may be made from any of a variety of materialsincluding metals, such as stainless steel or suitable plastic materials,or other suitable biocompatible materials (e.g., stainless steel,titanium, a cobalt chromium alloy, or the like). Those of skill in theart will also appreciate that a variety of mechanisms could be used toeffect the curvature other than a cable 168. For example, a shaft couldalso be used to push the flexible cannula 168 on the convex side of theshaft.

FIGS. 6A-6D show a hinged cannula 180 comprising mechanical linkage 182,with FIGS. 6A-6B showing the hinged cannula 180 with the joint 184 inthe straight position, and FIGS. 6C-6D showing the hinged cannula 180with the joint 184 in the angled configuration. As shown in FIGS. 6A-6D,the hinged cannula 180 may include a proximal end 186, a handle 188, anactuating rod 190, an outer tubular shaft 192, a mechanical linkage 182,a joint 184 (e.g., a pin hinge), and a distal leading end 194.Additionally, as FIGS. 6B and 6D show a cross-sectional view through thehinged cannula 190, an inner, hollow tubular shaft 196 is also shown.For the hinged cannula 180 to assume its angled configuration, as shownin FIGS. 6C-6D, the handle 188 may be slid longitudinally relative tothe outer tubular shaft 192 toward the proximal end 186 of the hingedcannula 180. The handle 188 may be coupled to the proximal portion ofthe rod 190 a, so movement of the handle 188 may also cause the rod 190to move. The distal portion of the rod 190 b may be coupled to themechanical linkage 182, so movement of the handle 188, and thus the rod190, would lead to the angulation of the mechanical linkage 182. Theangulation of the mechanical linkage 182 may also cause tire angulationof the joint 184, thereby making the hinged cannula 180 assume itsangled configuration. The tubular outer shaft 192 may have guide notches198 or other indicia near the handle 188, as shown in FIGS. 6A and 6C.Such notches or other indicia (e.g., markings) may aid the practitionerin knowing exactly what position the hinged distal leading end 194 isin, even without being able to physically see it.

FIG. 7 shows a scan similar to that of FIG. 5, illustrating an exemplarypathway that a hinged cannula 180 such as that of FIGS. 6A-6D may beadvanced along. The entry site 114 of the hinged cannula 180 may be onthe posterior surface of the patient's back at a location that islaterally offset from a patient's spinous process 116. The hingedcannula 180 may be initially inserted in its straight configuration, asshown in FIGS. 6A-6B, and the initial approach of the hinged cannula 180to the disc 104 may be a posterior approach (although offset therefrom)relative to the disc 104. When the hinged cannula 180 is in the regionof the patient's back about one or more of the erector spinae 106,quadratus lumborum 108, or psoas major 110 muscles, the mechanicallinkage 182 and joint 184 may be angulated, so the hinged cannula 180assumes its angled configuration, as shown in FIGS. 6C-6D. In its angledconfiguration, the hinged cannula's 180 approach to the disc 104 maydeviate from the posterior approach towards a lateral approach, and thedistal leading end 194 of the hinged cannula 180 may attach to thelateral aspect of the disc 104 directly, or nearly directly, lateral.Because the hinged cannula 180 is being advanced largely through onlymuscle tissue once actuation of the hinge mechanism may occur, themuscle tissue is typically easily parted, allowing passage even of thecannula 180 in its angulated configuration as seen in FIGS. 6C-6D. Inother words, the muscle tissue may typically be parted, providing apathway through which the leading distal end 194 of cannula 180, andnon-linear portions of angled shaft 192 may be advanced, as needed. Suchadvancement may occur while observing progress of the cannula inreal-time on a monitor (e.g., while watching a video feed of a scan orother image similar to that of FIGS. 1, 2A, and 7). The practitioner mayfind it beneficial to perform this procedure after the insertion of aflexible guide wire as previously described. The hinged cannula 180 maybe advanced over the flexible guide wire if desired by the practitioner.

After successful attachment to the lateral aspect of the disc 104, itmay be necessary to repeatedly change the hinged cannula 180 from thestraight to angled form to allow instruments used for clearing the discspace to be inserted and used. Alternatively stated, it may be necessaryto straighten out the hinged cannula 180 and pass a cutting tool pastthe pivot point 184 and then redirect the cutting device with thelinkage so that it enters the disc 104 laterally. This same process mayneed to be repeated to remove the tool and insert any straight implantsinto the disc space. As with any of the processes described herein, thisprocess may be performed with or without a flexible guide wire remainingin place. The hinged cannula 180 may be made from any of a variety ofmaterials including metals, such as stainless steel, plastics or otherbiocompatible materials (e.g., stainless steel, titanium, a cobaltchromium alloy, or the like). Those of skill in the art will alsoappreciate that a variety of mechanisms could be used to effect theangulation other than illustrated rod 190.

FIGS. 8A-8C show an exemplary pre-stressed cannula 200, which mayinclude a handle 202, an outer sleeve 204, an inner tubular shaft 206,and a leading distal end 208. As seen in FIG. 8C, the inner tubularshaft may include a portion that is pre-stressed 206 a (i.e., to defaultto assume a curved configuration) and a portion that is not pre-stressed206 b. FIGS. 8A and 8C show how the outer sleeve 204 may initially bepositioned over the pre-stressed portion 206 a to hold the pre-stressedportion 206 a in a straight configuration. FIG. 8B shows how the outersleeve 204 may be retracted from over the pre-stressed portion 206 a tothe portion that is not pre-stressed by sliding the outer sleeve 204longitudinally relative to the inner tubular shaft 206 toward the handle202. When the pre-stressed portion 206 a is no longer constrained by theouter sleeve 204, it can resume its default curved configuration. Aplurality of slots 272 similar to slots 172 of FIGS. 4B-4C are alsoshown in portion 206 a. Slots 272 are shown formed in both sides ofportion 206 a, although in some embodiments, they may only be presentwithin one side. Their presence in both sides may allow portion 206 a tobe curved in the opposite direction, as will be appreciated, althoughthe pre-stressing applied during manufacture may be such that theportion 206 defaults to curving to one side or the other, depending onselections made during manufacture. It is also anticipated that a rod,or other structure, could be placed on the inside or outside of apre-stressed component, such that when the rod was removed, thepre-stressed component would assume its curved shape.

Although FIGS. 2A-7 show the disc being approached laterally from theright of the patient, those of skill in the art will appreciate that theposterior to lateral approach could also be performed so as to approachthe disc laterally from the left of the patient.

FIG. 9A shows an exemplary cutting device 210 that may be used to clearthe disc space in an interbody fusion procedure. As shown, the cuttingdevice 210 may include a trigger mechanism 212, a drive shaft 214 inwhich at least a portion of the drive shaft is flexible, knobs 216, aninner shaft 218, and a blade 220. FIGS. 9B and 9C show a close up of thetrigger mechanism 212 associated with blade 220 at the distal end 214 aof the drive shaft, which may include a mechanism by which the angle ofthe blade 220 may be adjusted, by retracting, or extending the bladeinto a recess in distal end 214 a of shaft 214. Control of the degree ofsuch extension or retraction of blade 220 may be achieved throughmanipulation of structures 216, 218, and the like at proximal end 210 bof device 210.

As seen in FIG. 9B, the extensions 222 of the trigger mechanism 212 arefully retracted within the distal end 210 a of the cutting device, whichmay cause the blade 220 to be in a retracted position at the distal end210 a of the cutting device 210. The blade 220 may be in a retractedposition when the surgeon initially places the cutting device 210 nearor within the disc 104 (and as it is advanced thereto along the curvedor other non-linear posterior to lateral pathways described above).Before the cutting device 210 is used to clear the disc material of disc104, the surgeon may need to set longitudinal travel limits to ensurethat the cutting device 210, when cutting, does not advance or retractbeyond a designated safe area within the disc 104. Once this area oftravel has been determined (e.g., by consulting a pre-operative scan orother real-time image) and locked for safety, the cutting device 210 canbe rotated.

The inner shaft 218 may need to rotate with the blade 220 as the cuttingdevice 210 is used. In its retracted position, the blade 220 may beparallel, or nearly parallel, to the longitudinal axis of the shaft 214as shown in FIG. 9B. As the blade 220 is deployed, the angle between theblade 220 and the longitudinal axis of the distal end 210 a of thecutting device 210 may increase from the retracted position seen in FIG.9B towards an extended position seen in FIG. 9C. In FIG. 9C, the blade220 is shown extending approximately 90° in a sideways lateral directionfrom the distal ends 214 a and 210 a.

At some point, the blade 220 may make contact with the bony endplate ofthe vertebral body and encounter resistance, e.g., as the blade 220 isadvanced longitudinally within disc space 104 from the lateral aspectseen in the various Figures towards the opposite lateral end of disc104. The hardness of the endplate may subject the blade 220 to stresseswhich must be overcome by the cutting blade. For this reason, it may beadvantageous to only deploy blade 220 while the device is rotating at aspeed sufficient to provide momentum allowing the blade 220 to cutthrough the endplate without binding or breaking. As seen in FIG. 9C,the blade 220 is shown essentially perpendicular to the longitudinalaxis of the cutting device 210 and/or distal end 214 a. With the blade220 angled as desired and rotating at an appropriate speed, the surgeonthen advances at least blade 220 of the cutting device 210 forward ordraws it backwards until the cutting device 210 has created removed adesired amount or volume of material within the disc 104 that isacceptable to the surgeon. Increasing the deployment of the blade 220may increase the depth of the cut into the vertebral endplates. Whileshown with at or near 90° extension of blade 220, it will be appreciatedthat any angle between 1° and 90° (or even more than 90°) may bepossible, through manipulation of one or more of structures 216, 218 ofdevice 210. A full 90° extension of blade 220 results in a cylindricallyshaped cut in disc 104 having the maximum diameter. Partial retractionto an intermediate angle (e.g., 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°or 80°, or over extension past 90° by such forgoing amounts will reducethe diameter of the resulting cylindrical cut.

The surgeon may elect to retract or partially close the blade 220 as heor she reaches the predetermined endpoints of travel for an increasedmargin of safety. The cutting device 210 itself may contain somemechanism (e.g., a mechanical stop) that sets limits to the travel ofthe cutting device 210, such as safety pins, or an adjustable slot.While the term “blade 220” is principally used herein, it will beappreciated that the cutting device may include one or more blades.

The conscientious practitioner will wish to avoid the one or morecutting blades from cutting outside the safe confines of the disc spacewhere they could create injury to the surrounding structures. For thisreason, stops may be set to avoid traveling too far forward, and thusexiting the opposite side of the disc, as well as to avoid pulling thecutting device back into the cannula. These stops can be achieved in avariety of ways such as by adding pins which limit the travel of thecutting device. In FIG. 9A, stops could be placed onto a geared rail toaccomplish this purpose, as shown in further detail in provisionalapplication 62/382,007 filed Aug. 31, 2016. Other methods are easilyconsidered, such as slots of a specified length that limit the travel ofthe cutting device. It would be most prudent for the practitioner to setthe stops as desired prior to rotation of the cutting device 210.

In FIGS. 10A-10C, another cutting device 210 is illustrated. Cuttingdevice 210 may include one or more blades 220 for cutting, and one ormore slots 219 for limiting the travel of the cutting device during itsoperation. The practitioner selects the appropriate length of the slotfor cutting and then centers the slot within the disc space prior tocutting by manipulating a threaded depth adjustment or similaradjustment. For example, ring 218 a may be rotated to shorten orlengthen the resulting cutting distance. Graduated length measurementsmay be provided on the shaft on which ring 218 a threadably rotates upand down the underlying shaft. A pin 218 b may be inserted to serve as astop in conjunction with the illustrated slot to also aid in limitingthe travel distance. FIGS. 10A-10C shows progression as the practitionerpulls the cutting device back from the far side of the disc space,towards the near side of the disc space (e.g., FIG. 10A shows whereblade 220 is at the far side, FIG. 10C shows the entire cutting spacehaving been traversed, and FIG. 10B is intermediate the two). As shown,in FIG. 10C, pin 218 b is against the forward end of the slot,preventing further pull back without removal of the pin. Further detailsof exemplary stop mechanisms are disclosed in provisional application62/382,007 filed Aug. 31, 2016, to which the present application claimspriority.

The illustrated cutting device may be cannulated to work over a flexibleguide wire. In this case, the guide wire may be first passed fullyacross the disc space unit the leading end of the guide wire exits theopposite lateral side of the disc space substantially equidistant fromthe front and back walls of the disc. The guide wire may remain in thisposition while the cutting process proceeds. The guide wire helps tomaintain the cutting device centered in the disc space while the cuttingis accomplished. FIGS. 11A-11C illustrate use of such a guide wire. Theslots help to prevent the practitioner from advancing the cutting devicepast the confines of the disc and from pulling the cutting device intothe cannula while cutting. To further reduce the risk of the cuttingdevice deviating from the desired cutting zone, it is suggested thatcutting be accomplished only while the practitioner is pulling thecutting device back through the disc, rather than pushing the deviceforward.

Those of skill in the art will appreciate that a variety of methods maybe used to deploy the blade 220 other than the illustrated mechanism,including a rotating knob on a threaded sleeve, such as a triggermechanism shown in FIGS. 10A-10C. Other mechanisms will be apparent tothose of skill in the art in light of the present disclosure. Therotation of the cutting device 210 may be done by hand, or moretypically with the assistance of a power source. The rotation of thecutting device 210 will typically occur at higher speeds than cannotnormally be accomplished by hand. A standard drill head, commonly foundin the operating room would be sufficient for the procedure. The cuttingdevice 210 may attach to the drill head or other rotational source via a¼ inch quick connector 222 (FIG. 9A), or similar connection. Increasingthe RPM of the cutting device 210 may improve the effectiveness of theblade 220 by using the momentum of the system to cut through the discmaterial, cartilage and bone.

Once the blade 220 has cut through the disc material and endplates tothe satisfaction of the surgeon, the cutting device 210 may be removed.The blade 220 may be restored to its retracted position on the distalend 210 a of the cutting device 210. Once the blade 220 has beenretracted, the cutting device 210 may be withdrawn.

The cutting device 220 may contain one or more blades. The blades may bedesigned to function with cutting or grinding action, or both. Theblades may be manufactured from a high strength material such asstainless steel, or other materials such as carbon fiber, other metals,suitable plastics, or other biocompatible materials (e.g., titanium, acobalt chromium alloy or the like). The cutting blades may be changed orreplaced easily, as needed.

Although cutting device 210 is described in the context of the posteriorto lateral approach for an interbody fusion, those of skill in the artwill appreciate that the cutting device 210 could be used to clear thedisc space after another method was employed to access the disc 104(e.g., a lateral approach technique).

Embodiments herein are principally described in which the tool isadvanced along the desired path towards the lateral aspect of the disc,and during such advancement, or even after such advancement, deviatingfrom the typically straight posterior or posterolateral path to alateral, or substantially lateral path. Such deviation may occur duringadvancement, after advancement, or anywhere therebetween. For example,deviation may occur as the leading end of the tool approaches, reaches,or nearly reaches the lateral aspect of the disc. Approaching or nearlyreaching the lateral aspect of the disc may be, e.g., within about 1 cmof the lateral aspect of the disc, within about 5 mm, within about 3 mm,or within about 1 mm of the disc.

The procedures described herein may be performed with the assistance offluoroscopy or similar real-time imaging to avoid damage to the adjacentvital structures including: the vena cava, iliac veins, nerve roots andthecal sac within the spinal canal. Neuromonitoring may also be employed(e.g., throughout the procedure, including during placement of thecannula, as well as while the disc space is cleared) to detect anyinappropriate interaction with the neurological structures.

Numbers, percentages, or other values stated herein are intended toinclude that value, and also other values that are about orapproximately the stated value, as would be appreciated by one ofordinary skill in the art encompassed by embodiments of the presentdisclosure. A stated value should therefore be interpreted broadlyenough to encompass values that are at least close enough to the statedvalue to perform a desired function or achieve a desired result. Thestated values include at least the variation to be expected in asuitable manufacturing process, and may include values that are within25%, within 20%, within 10%, within 5%, within 1%, etc. of a statedvalue. Furthermore, the terms “substantially”, “similarly”, “about” or“approximately” as used herein represents an amount or state close tothe stated amount or state that still performs a desired function orachieves a desired result. For example, the term “substantially” “about”or “approximately” may refer to an amount that is within 25%, within20%, within 10% of, within 5% of, or within 1% of, a stated amount orvalue.

Ranges between any values disclosed herein are contemplated and withinthe scope of the present disclosure (e.g., a range defined between anytwo values (including end points of a disclosed range) given asexemplary for any given parameter).

As used in this specification and the appended claims, the singularforms “a,” “an” and “the” include plural referents unless the contextclearly dictates otherwise.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A method for accessing a disc of a patient'svertebrae of the patient's spine as part of a discectomy or spinalinterbody fusion, the method comprising: inserting a leading end of atool into a posterior surface of the patient's back at a location on theposterior surface that is laterally offset from the patient's midline,the insertion being along a path that begins as a posterior orposterolateral approach to the disc; advancing the tool along the pathtowards the disc, the path deviating from the posterior orposterolateral approach towards a lateral approach as the tool isadvanced from the posterior or posterolateral surface until it reaches alateral aspect of the disc; using the tool to access the disc throughthe psoas muscle of the patient; and performing at least a portion ofthe discectomy or spinal interbody fusion; wherein the tool comprises aflexible cannula that is flexible so as to be selectively straight orcurved, the cannula being initially inserted into the patient's back inthe straight configuration during initial approach to the disc, thecannula being made to curve during advancement as it advances towardsthe lateral aspect of the disc.
 2. A method as in claim 1, whereininserting and advancing the tool is performed under fluoroscopy.
 3. Amethod as in claim 1, wherein the path passes through muscles of thepatient, avoiding a spinal canal, other nerves, and bone of the patient.4. A method as in claim 1, wherein the flexible cannula comprises acable which can be selectively actuated to cause the cannula to assumethe curved configuration.
 5. A method as in claim 1, wherein the toolcomprises or is used with a hinged cannula, the hinged cannula beinginserted posteriorly from a position offset some distance lateral to amidline of the patient's spinous process, the hinged cannula comprisinga mechanical linkage which is employed during advancement to orient thecannula laterally relative to the disc space.
 6. A method as in claim 1,wherein the tool comprises or is used with a pre-stressed cannulaincluding an outer sleeve, an inner piece, or both, which holds thepre-stressed cannula in an initially straight position, the pre-stressedcannula being inserted posteriorly from a position offset some distancelateral to the midline, the outer sleeve and/or inner piece of thecannula being retracted during or after advancement to orient thecannula laterally relative to the disc space.
 7. A method as in claim 1,the method further comprising clearing a disc space of the disc with arotating cutting device, the rotating cutting device being advancedalong the same path along which the tool was advanced towards the disc.8. A method for accessing a disc of a patient's vertebrae of thepatient's spine as part of a discectomy or spinal interbody fusion, themethod comprising: inserting a leading end of a tool into a posterior orposterolateral surface of the patient's back at a location on theposterior or posterolateral surface that is laterally offset from thepatient's midline, the insertion being along a path that begins as aposterior or posterolateral approach to the disc; advancing the toolalong the path until it approaches, reaches, or nearly reaches thelateral aspect of the disc; adjusting the tool such that the end of thetool is oriented laterally or substantially laterally relative to thedisc and; using the tool to access the disc through the psoas muscle ofthe patient; wherein the tool comprises a flexible cannula that isflexible so as to be selectively straight or curved, the cannula beinginitially inserted into the patient's back in the straight configurationduring initial approach to the disc, the cannula being made to curveduring advancement as it advances towards the lateral aspect of thedisc.
 9. A method as in claim 8, wherein the tool is advanced over arigid or flexible guide wire.
 10. A method for accessing a disc of apatient's vertebrae of the patient's spine as part of a discectomy orspinal interbody fusion, the method comprising: from a preoperativescan, measuring a distance from a specified location between a skinsurface and the disc; securing a device over a posterior surface of thepatient's back with a tool coupled to the device, the device includingan arm having a length that is based on the measured distance; insertinga leading end of the tool into the posterior or posterolateral surfaceof the patient's back and advancing the tool along a predetermined paththat begins as a posterior or posterolateral approach to the disc, saidpath being along the circumference of a circle the radius of which issubstantially the measured distance; advancing the tool along thepre-determined path which will deviate from a posterior orposterolateral orientation towards a lateral orientation relative to thedisc as the tool advances, or after the tool has advanced, from theposterior or posterolateral surface through the psoas muscle of thepatient until it has reached, or nearly reached, a lateral aspect of thedisc; and using the tool or a subsequent tool to access the disc andperform at least a portion of the discectomy or spinal interbody fusion.11. A method as in claim 10, wherein the tool comprises or is used witha cannula.
 12. A method as in claim 10, wherein the device is securedover the posterior or posterolateral surface of the patient's back at alocation that is offset some distance laterally from a midline of thepatient, and the tool is advanced by rotation through the predeterminedpath, the predetermined path being an arc length of a circle having aradius based substantially on the measured distance from the specifiedlocation between the skin surface and the disc.
 13. A method as in claim10, wherein the distance that the device is offset laterally from themidline is substantially equal to a measured radius of the disc.
 14. Amethod as in claim 10, wherein the device is secured over the posteriorsurface of the patient's back at a location that is over the midline,and the tool is advanced by rotation through the predetermined path, thepredetermined path being an arc length of a circle having a radius basedsubstantially on the measured distance from a tip of the spinal processto the center of the disc.
 15. A method for accessing a disc of apatient's vertebrae of the patient's back as part of a discectomy orspinal interbody fusion, the method comprising: from a preoperativescan, measuring a distance from a desired reference point between thespinous process and the surface of the skin to the disc; securing aguiding device over a posterior surface of the patient's back, theguiding device including a guide indicating a radius of curvaturesubstantially based on said distance that directs a tool towards thelateral aspect of the disc; inserting a leading end of the tool into theposterior or posterolateral surface of the patient's back along apredetermined path, as determined by the guiding device that begins as aposterior or posterolateral approach to the disc; advancing the toolalong the predetermined path which deviates from the posterior approachtowards a lateral approach as the tool is advanced from the posteriorsurface towards a lateral aspect of the disc; and using the tool, or asubsequent tool, to access the disc through the psoas muscle and performat least a portion of a discectomy or a spinal interbody fusion.
 16. Amethod as in claim 15, wherein the tool comprises or is used with acannula.
 17. A method as in claim 15, wherein the guiding device issecured over the posterior surface of the patient's back at a locationthat is offset some distance laterally from the midline, and the tool isadvanced by rotation through a predetermined path, the predeterminedpath being an arc length of a circle having a radius based substantiallyon a measured distance from the spinous process to the center of thedisc.
 18. A method as in claim 15, wherein a distance that the guidingdevice is laterally offset from the midline is substantially equal tothe measured distance between the reference point and the disc.
 19. Amethod as in claim 15, wherein the reference point is a tip of thespinous process of the patient, and the measured distance is a distancefrom the tip of the spinous process to the center of the disc.
 20. Amethod as in claim 15, wherein the guiding device is secured over theposterior surface of the patient's back at a location that is offsetsome distance laterally from the midline, and the tool is advanced byrotation through a predetermined path, the predetermined path being anarc length of a circle having a radius based substantially on themeasured distance from the skin surface to the center of the disc.